Thermolytic pyrolysis processes

Bergougnou and co-workers (Mok et al., 1984 Graham et al., 1986 Berg et al., 1986) have developed, in the course of their work on the pyrolysis of wood, cellulose and hydrocarbons, a terminology to deal with the increasing severity of the thermolytic pyrolysis processes. Slow pyrolysis is defined as a process which takes place at temperatures less than 500°C, in which the feedstock is heated at low rates (< 2°C/s), and in which the reactant resident times are measured in the scale of minutes to hours. 

The application of thermolytic reactions (e.g. Diels-Alder and reverse Diels-Alder processes) for the synthesis of fluoro-organic compounds has been reviewed. The cycloaddition of the meso-ionic dithiolone or thiazolone compounds (209 X = S or NPh) with the Diels-Alder adduct of cyclo-octatetraene and dimethyl acetylenedicarboxylate occurs at the cyclobutene ring to give the exo-adducts (210). Pyrolysis of compounds (210) yields dimethyl phthalate and 7,9-diheteratricyclo[4,2, 1,0 ]non-3-en-8-ones (211 X = S or NPh) by retro-[4-t- 2] addition. The similar additions of (209) and related compounds to dimethyl 7-oxabicyclo[2,2,l]-hepta-2,5-diene-2,3-dicarboxylate afforded [4 -1-2] adducts which on pyrolysis suffered double thermal fragmentation e.g. loss of XCO and 3,4-dimethoxycarbonyl-furan) to afford five-membered aromatic heterocyclics. ... 

The first step of the process is the homolysis of the P-H bond. Due to the respective volatilities of the solvent (toluene) and of the phosphonate, a thermolytic mechanism in the vaporous phase of the bubble seems unlikely (Fig. 22). Pyrolysis of dimethyl phosphonate gives methylphosphonic acid, probably via an intramolecular Arbuzov reaction. On the other hand, y-radiolysis and UV... 

Pyrolysis is not combustion but involves rather a complex set of reactions that depend both on the plastics involved and the precise nature of the thermolytic process used. Possible reaction pathways are ... 

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